1. Field of the Invention
The present invention relates to an image forming apparatus and, more particularly, to an image forming apparatus capable of shortening a document size detection time.
2. Description of the Related Art
As a typical image forming apparatus, an electronic copying machine can be used. The electronic copying machine has a scanning unit for scanning a document. The scanning unit is provided with a carriage. During a copying operation, the scanning unit is moved by the carriage to a predetermined position (or a home position according to a magnification) in accordance with a paper size or a copying magnification. Normally, since the scanning unit is provided with an scale indicator, a distance from a scanning start position to the home position can be detected using the scale. This distance represents a copying range determined in correspondence with the size of a copy paper sheet on which a document image is to be formed. Then, the size of a placed document is detected in order to perform a copying operation according to a magnification. In this case, the scanning unit is moved from the home position (position indicating a copying range) to the scanning start position. Thereafter, an end portion of the document is detected while moving the scanning unit from the scanning start position in the scanning direction, thus determining a document size.
However, such document detection requires much time since the scanning unit is once returned to :he scanning start position and is then moved therefrom in the scanning direction.
A so-called continuous page copying operation is sometimes performed using the above-mentioned electronic copying machine in order to obtain copies of two open pages. In a copying machine having a continuous page copying function, images can be formed on corresponding copy paper sheets from two documents by depressing a copy key once after the continuous page copying mode is selected, without using optional equipment such as an automatic document feeder. However, when a normal copying operation is to be executed after the continuous page copying operation, an operator often may not cancel the continuous page copying mode. In this case in the above-mentioned document size detection method, the continuous page copying function is not automatically canceled, and a new continuous page copying operation is executed. Thus, a copying operation is performed for the second imaginary document. Therefore, an unnecessary blank copy is outputted.